Here's the page, for flows on the North Fork check "NF @ Banks." Payette River Flows - Kayak Idaho
Above 400 is creeky fun on the Upper 5 if it is not covered with snow. My personal minimum for the Lower 5 is about 1,000 just because it's so wide and boney below that. The middle is doable at these flows, but its definitely boat abusive and, in my opinion, pretty sketch due to lots of pin potential.